1. Field of the Invention
The present invention relates to an electrochemical cell designed for improving energy density by forming a prismatic case of at least two stamped metal components mated to reduce cell size. More particularly, the present invention relates to an electrochemical cell housed in a casing of mated stamped metal halves that may have a recess or indentation provided in the body of at least one of the casing components.
2. Prior Art
Lithium anode based electrochemical cells, such as silver vanadium oxide cells used in implantable medical device applications, are typically housed in cylindrical and prismatic casings. Both of these housing designs comprise two main components, a lid and a deep drawn case.
For example, the prior art reveals U.S. Pat. No. 6,004,692 to Muffoletto et al., assigned to the assignee of the present invention and incorporated herein by cell housed in a prismatic casing enclosure for lithium electrochemical cell. The cell includes a deep drawn conductive casing having an open end closed by a connected lid. The lid is provided with a terminal pin serving as a lead for making electrical connection to a load. The casing itself provides the other terminal for the cell. The generally prismatic or rectangular shape of the Muffoletto et al. casing makes it extremely difficult, if not impossible, to provide indentations or recesses in the casing side wall while simultaneously inserting a cell stack with the case in an efficient manner. Such recesses are useful for nesting components of the device being powered by the cell.
The use of casing halves constructed of resin materials is also known in the prior art. For example, U.S. Pat. No. 4,659,636 to Suzuki et al. relates to a sealed storage battery housed inside casing halves molded from a synthetic resin. A suitable synthetic material is a composition containing blended ABS and polycarbonate resins.
Also, dipping battery elements in liquid thermoplastic encapsulating materials has been described. For example, U.S. Pat. No. 5,270,133 to Baumann III describes a case-less battery wherein the electrode elements are housed in an encapsulating material. The electrode elements are encapsulated by dipping them into air or heat curable thermoplastic materials.
Also, the use of a sealing bag in a non-aqueous electrolyte battery is known. For example, U.S. Pat. No. 6,404,693 to Fukuda et al. describes a non-aqueous electrolyte cell having electrode elements house in a sealing bag whose peripheral parts are heat fused together. The sealing bag is formed from a film having a multilayered configuration including a metal layer (metal foil) and an electrolytic solution insulating barrier layer.
The problem with the prior art constructions is that synthetic materials are not suitable for providing a hermetic enclosure, especially for an electrochemical cell intended to power an implantable medical device. Also, a prismatic or cylindrically-shaped casing may not be acceptable in all instances, for example in batteries powering implantable medical devices where it is desirable to have an indentation in the body of the casing for nesting components of the medical device. What is needed is a new casing construction of stamped metal components which allows for greater flexibility in package shape than is offered by traditional designs. These battery cases permit the cell designs to be much more flexible in nature while allowing for extremely energy efficient designs.
Accordingly, the present invention is directed to an electrochemical cell having plate electrodes housed inside mating xe2x80x9cclam shellxe2x80x9d casing components. Also, the present casing design allows for indentation structures in the casing components by virtue of them being stamped metal parts. Depending on the design, some of these indentations are not possible with traditional cylindrical and prismatic casing designs. When mated together, the casing components are form-fitting with respect to the internal battery structure so as to reduce the overall size of the electrochemical package. This provides the cell with the greatest amount of energy per unit size.
The foregoing and additional advantages and characterizing features of the present invention will become clearly apparent upon reading of the ensuing description together with the included drawings wherein: